Volume rendering refers to a set of computer graphic techniques used to display a 2D projection of a 3D discretely sampled data set. The contents of this data set are dependent on the acquisition source of the data. For example, in the domain of medical imaging, the 3D data set typically includes a plurality of 2D slice images acquired by a Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scanner.
Ultra-realistic volume rendering can provide maximal benefits in distinguishing fine tissue characteristics in medical imaging. Quite often, the user needs to carefully window and level the rendering transfer function to fine tune the data to reveal the salient information. For instance, an image may reveal lesions within the liver or fine lung structure only within a very narrow range of intensity values.
Unfortunately, conventional ultra-realistic volume rendering technologies today are based on path tracing or ray tracing and, as such, requires many compromises on quality during interactions on most computing systems. This greatly limits the usability of such rendering for precision windowing. Thus, it is desired to improve rendering speed when changing transfer function and window levels, without sacrificing quality.